HYDROGEN AND ITS COMPOUNDS

Transcription

1 HYDROGEN AND ITS COMPOUNDS Short Answer Questions: 1. Write any two methods for the preparation of H 2 O 2? Ans. I) Electrolytic Method: Hydrogen peroxide is manufactured on a large scale by the electrolysis of 50% sulphuric acid using platinum anode and lead cathode followed by vacuum distillation. A current of high density is used for electrolysis. At cathode hydrogen gas is liberated and at anode peroxy disulphuric acid is formed. - 2H2SO4 2H+ + 2HSO 4 - At anode: 2HSO 4 H 2S2O8 + 2e At cathode: 2H+ + 2e H2 i. On distillation Peroxydisulphuric acid undergoes hydrolysis to give hydrogen peroxide. H2S2O8 + H2O H 2SO5 + H2SO4 H2SO5 + H2O H2O2 + H2SO4 ii. Industrially H2O2 is prepared by auto oxidation of 2-alkyl anthroquinone. 2-ethyl anthroquinol O (air) 2 + H O 2 ethylanthroquinone H /Pd Write any two oxidising properties and two reducing properties of H 2 O 2 with equations. Ans. Oxidising Properties: i. It oxidises ferrous salts to ferric salts in acidic medium (aq) + (aq) + 2 2(aq) (aq) + 2 (l) 2Fe 2H H O 2Fe 2H O ii. It oxidises black lead sulphide to white lead sulphate. PbS(s) + 4H2O2 (aq) PbSO4 (s) + 4H2O (l)

2 iii.. It oxidises ferrous salts to ferric salts in basic medium (aq) + 2 2(aq) (aq) + (aq) 2Fe H O 2Fe 2OH Reducing Properties: i. It reduces HOCl into Cl. HOCl + H2O2 H3O+ + Cl + O2 ii. It reduces acidified potassium permanganate tocolourless Mn +2. 2MnO H + + 5H2O2 2Mn H2O + 5O2 iii. In alkaline solution it reduces potassium permanganate to manganese dioxide. 2MnO H2O2 2MnO2 + 2OH - + 2H2O + 3O2 3. What do you mean by hardness of water? Give the reactions in the Ion-exchange method. Ans. A sample of water which does not give good lather with soap is known as hard water. Hardness of water is of two types: a) Temporary hardness (It is due to presence of bicarbonates of calcium and magnesium) b) Permanent hardness. (It is due to presence of chlorides and sulphates of calcium and magnesium) permutit process : Permutit is artificial zeolite. Chemically it is hydrated sodium aluminium orthosilicate (Na2Al2Si2O8.xH2O).Calcium and magnesium ions which cause hardness in water are replaced by sodium ions which do not cause hardness. Thus water is softened. This method is called Ion- exchange process. Na2Al2Si2O8.xH2O + M2+ MAl2Si2O8.xH2O + 2Na+. Here M2+ is Ca2+ or Mg2+. After some use, all the sodium ions in the permutit are replaced by Ca2+ or Mg2+ ions and then it is said that permutit is exhausted. The exhausted permutit can be regenerated by soaking it with 10% brine (NaCl solution). Chemical reaction during the revival of exhausted permutit is given as MAl2Si2O8.xH2O + 2Na+ Na2Al2Si2O8.x H2O + M2. Here: M2+ is Ca2+ or Mg2+

3 4. Write a few lines on the utility of hydrogen as fuel? (March 2013) Ans. i) Hydrogen is widely used as an industrial fuel as its heat of combustion is higher than other fuels like LPG, methane,petrol etc. ii. Pollutants in combustion of Hydrogen are only the oxides of Nitrogen which are easily removed by injecting small amount o f water in to Hydrogen cylinder. Thus it is a better fuel than petrol. iii. It is used in Fuel cells for generating electricity. iv. The atomic hydrogen and Oxy Hydrogen torch are used for welding purposes and for melting platinum metal and quartz. v. Liquid hydrogen is used as rocket fuel. 5. Complete and balance the following chemical equations: a) PbS+H 2 O 2 b) MnO H 2 O 2 c) CaO+H 2 O d) Ca 3 N 2 +H 2 O Ans: a) PbS(s) + 4H2O2 (aq) PbSO4 (s) + 4H2O (l) b) 2MnO H + + 5H2O2 2Mn H2O + 5O2 c) CaO+H 2 O Ca (OH) 2 d) Ca3N2 + 6H2O 3Ca (OH)2 + 2NH3

4 Very Short Answer Questions 1. Write any two uses of D2O. Ans. It is extensively used as moderator in nuclear reactors and in exchange reactions for studying reaction mechanisms 2. What is deuterolysis? Give an equation for Deuterolysis? Ans. The reaction of salts with heavy water is called deuterolysis. AlCl3 + 3D2O Al (OD)3 + 3DCl BiCl3 + D2O BiOCl + 2DCl 3. Draw the structure of H 2 O 2. gas PHASE SOLID PHASE 4. Write any two modern uses of H 2 O 2 Ans. 1. It is used in the manufacture of chemicals like sodium perborate and per carbonate which are useful in making high quality detergents. 2. It is used in manufacture of hydroquinone, tartaric acid and Pharmaceuticals (Cephalosprin). 5. What is perhydrol? Give its volume strength? Ans. A 30(w/v) % solution of hydrogen peroxide is called as perhydrol. Its volume strength is 100 volumes

5 6. Give the melting point and boiling point of D 2 O? Ans. Freezing point of D 2 O is C Or K and Boiling point is C or K 7. What is meant by coal gasification? Give relavent equation? Ans. The process of producing syngas from coal is called coal gasification. C + H2O 673K CO Catalyst + H2 The production of hydrogen can be increased by reacting carbon monoxide of syngas mixture with steam in the presence of iron chromate as catalyst. CO + H2O Fe 450 CO2 + H2 2O3 / Cr 0 C 8. What do you mean by autoprotolysis? Give the equation to represent the auto protolysis of water. Ans. The self ionisation of water is called auto protolysis. H O + H O H O + OH + 2 ( l ) 2 ( l ) 3 ( aq) ( aq) 9. Water behaves as amphoteric substance in the bronsted sense? Explain. Ans. H2O has the ability to act as a Bronsted acid when dissolving alkalies and as a Bronsted base When an acid is dissolved in it. This is due to the autoprotolysis, H O + H O H O + OH + 2 ( l) 2 ( l ) 3 ( aq) ( aq) 10). Explain the term SYNGAS? Ans. The mixture of CO and H 2 is called water gas or synthesis i.e. syngas. It is used as a fuel gas.